There has been known a treatment method whereby an affected part of a patient of cancer, and so forth is irradiated with a charged particle beam (an ion beam) of a proton, a carbon ion, and so forth. A charged particle beam irradiation system (a particle beam emitting apparatus, or a charged particle beam emitting apparatus) for use in this treatment is provided with a charged particle beam generation unit, and a charged particle beam accelerated by the charged particle beam generation unit reaches an irradiation unit provided at a rotary gantry via a first transport system, and a second transport system provided at the rotary gantry, whereupon the charged particle beam emitted from the irradiation unit to irradiate the affected part of a patient. A double scatterer method (Non-patent Document 1, p. 2081, FIG. 35) whereby a beam is expanded by use of a scatterer to be subsequently cut out so as to match with the shape of an affected part, a wobbler method ((Non-patent Document 1, p. 2084, FIG. 41), and a scanning method ((Non-patent Document 1, pp. 2092 and 2093) for causing a fine beam to scan within an affected part have been known as a beam irradiation method of the irradiation unit.
Attention has been focused on the scanning method among those beam irradiation methods because the scanning method has a feature that an effect on a normal cell is less, and equipment incorporating a nozzle is unnecessary. It is the feature of the scanning method that outputting of a charged particle beam is stopped in response to a dose to an irradiation subject, an irradiation position of the charged particle beam, called a spot, is changed by controlling energy, and a scanning electromagnet, and emission of the charged particle beam is resumed after completion of such a change, thereby irradiating the irradiation subject (the affected part) with the beam so as to match with the shape of the irradiation subject, while sequentially changing over the irradiation position.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-175829    [Non-patent Document 1] REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 64, No. 8 (August, 1993), pp. 2074-2093